I. Technical Field
This invention relates, in general, to the fabrication of semiconductor devices. More particularly, this invention relates to the creation of features on semiconductor devices having sublithographic dimensions.
II. Background Art
Semiconducting microchips have become an integral part of everyday life. Semiconducting microchips are used in everything from toys to garage door openers, and most particularly in computers. The semiconductor industry has relentlessly sought to increase the speed at which a chip may function. One way to increase the speed at which a chip operates is to decrease the size of the circuit components in a logic chip. Decreased logic component size allows each component to operate more rapidly, as an electrical signal may traverse the circuit component in less time.
The components of a chip are created using a process known as photolithography. Conventional photolithography works by placing appropriate materials and light sensitive chemicals known as photoresists, or simply "resists", on the surface of a semiconductor wafer and then selectively exposing portions of the surface of the semiconductor wafer to light of a carefully selected wavelength. Various chemical processes allow materials to be added or removed at a location depending upon whether the location was exposed to light of particular wavelength. A particular area is exposed or not exposed by placing a mask between the light source and the wafer's surface. The mask allows light to pass through at certain points and blocks light at other points, thus printing a pattern on the surface of the wafer.
Conventional photolithography is limited by the diffraction effects of light passing through the mask. Due to the wave nature of light, any image made using a mask will be somewhat blurred by diffraction effects. This blurring due to diffraction effects is insignificant for large images. However, as the size of images shrink this blurring becomes more and more significant, until the image itself is obliterated by the blurring. Thus, conventional photolithography using a mask is practical only down to certain lower limits. Those limits are presently being reached. This blurring due to diffraction is one of the grave obstacles to the further miniaturization of circuitry on microchips. While image enhancement techniques have been developed to overcome, to a degree, the diffraction effects that distort an image, there still exists an image size below which traditional photolithography cannot function. To somehow go beyond the lower limits of traditional photolithography would allow the size of logic circuit components to be reduced, thus increasing the operating speed of the resulting semiconductor chips.